Reactivation of Human Cytomegalovirus (HCMV) from latency is the most common infectious complication in bone marrow transplant patients, with significant morbidity and mortality. Very little is known about the viral/host interactions governing the establishment and maintenance of long term HCMV infection. The long-term goal is to identify the viral and host mechanisms that lead to the development of CMV latency. The objective of this proposal is to determine the role of the CMV-encoded chemokine receptors in the establishment of latency in progenitor myeloid lineage cells and to identify the host signaling pathways that promote CMV establishment of latency. The central hypothesis is that the CMV-encoded chemokine receptors activate host signaling pathways which aid in the establishment of latency during in vivo infection. Project Summary: Our hypothesis is based on strong preliminary data which demonstrates that murine CMV (MCMV) lacking M33 does not efficiently establish latent infection and that M33-deficient viruses which express the HCMV-encoded chemokine receptors, UL33 or US28, complements this latency defect in vivo. Three specific aims will be pursued: 1) Identify the myeloid lineage cell type which requires M33 for the establishment and/or maintenance of CMV latency in vivo, 2) Identify the mechanisms underlying the role of M33 during infection in monocytes, and 3) Identify the M33-mediated signaling pathway (s) required for establishment and/or maintenance of CMV latency. This aim will utilize specific M33 mutant viruses coupled with microarray analysis to identify signaling pathways which are modulated by M33 and US28. The approach is innovative, and uses a multifaceted approach to identify the host and viral factors involved in the establishment and/or maintenance of CMV latency in myeloid lineage cells. The proposed research is significant, because it is expected to lead to the development of therapeutic strategies aimed at preventing CMV latency and complications due to reactivation of latent CMV. Relevance to Public Health: The new knowledge obtained will lead to the prevention of CMV latency and reactivation in immunocompromised patients, such transplant patients, neonates, and AIDS patients, where CMV infection leads to significant morbidity and mortality.